The present invention relates to an ink jet recording apparatus such as an ink jet printer or an ink jet plotter. More particularly, the present invention relates to the structure of a recording head in an ink jet recording apparatus.
Hitherto, in an ink jet recording apparatus such as an ink jet printer or an ink jet plotter, as shown in FIG. 12, in a drive signal generating circuit 8 formed in a apparatus main unit 2, a drive signal COM generated by a waveform generating circuit 80 is amplified by a current amplification circuit 89 using push-pull-connected transistors, etc., for example, then is output to a recording head 10 mounted on a carriage. The recording head 10 is provided with a plurality of pressure generating elements 17 for jetting ink drops from nozzle openings by pressurizing ink in pressure generating chambers and a head drive circuit 18 for selecting which of the plurality of pressure generating elements 17 to drive based on recording data, and the drive signal COM is applied to the pressure generating element 17 selected by the head drive circuit 18. As a result, the selected pressure generating element 17 pressurizes ink in the corresponding pressure generating chamber for jetting ink as an ink drop from the nozzle opening.
Here, the apparatus main unit 2 and the recording head 10 are connected by a flexible wiring board 100 having a length sufficient for the carriage to move, and the drive signal generating circuit 8 formed in the apparatus main unit 2 outputs a signal to the recording head 10 via the flexible wiring board 100.
FIGS. 13(A) and (B) show an example of a schematic structure of the recording head 10 in the conventional art. As shown in FIGS. 13(A) and (B), the recording head 10 has a flow passage unit 230, which comprises a nozzle plate 233 provided with a plurality of nozzle openings 231 as nozzle rows 232, a flow passage formation board 237 comprising pressure generating chambers 234 communicating with the nozzle openings 231 and reservoirs 236 for supplying ink to the pressure generating chambers 234 through ink supply ports 235, and an elastic plate 240 for abutting the tip of each piezoelectric vibrator 239 in a vertical vibration mode of piezoelectric vibration units 238 corresponding to the pressure generating elements 17 previously described with reference to FIG. 12 for expanding or shrinking the pressure generating chamber 234, the nozzle plate 233, the flow passage formation board 237, and the elastic plate 240 being stacked in one piece. The flow passage unit 230 is connected to a holder 241 formed by injection molding, etc., of a polymeric material and each piezoelectric vibration unit 238 is connected to a flexible cable 242 for communicating an external drive signal, then they are housed in a housing chamber 243, the abutment faces (not shown) against the holders 241 are fixed with an adhesive, and a frame 244 also serving as a shield material is inserted into the nozzle plate 233, forming the recording head 10. The holder 241 is provided with an ink lead passage 245 communicating with an external ink tank (not shown) and the tip is connected to an ink introduction port 246 of the flow passage unit 230 for supplying ink from the ink tank to the flow passage unit 230.
Each piezoelectric vibrator 239 in the vertical vibration mode forming a part of the piezoelectric vibration unit 238 is formed by stacking an electrode as one pole and an electrode as an opposite pole like a sandwich via a piezoelectric material, exposing one electrode to the tip side and the opposite electrode to the rear end side, and connecting to a segment electrode and a common electrode on each end face with piezoelectric constant d31, for example, although not shown, and is fixed to a fix board 247 matching the arrangement pitch of the pressure generating chamber 234 as a part of the piezoelectric vibration unit 238.
The segment electrode and common electrode (not shown) of each piezoelectric vibrator 239 of the piezoelectric vibration unit 238 are connected to a conductive pattern for drive signal transmission of the flexible cable 242 via a solder layer. With the flexible cable 242, a window 248 is formed in an area facing the fix board 247, a semiconductor IC (integrated circuit) 249 provided with the head drive circuit 18 (see FIG. 12) for converting a print signal into a drive signal for driving each piezoelectric vibrator 239 is installed in the window, and the print signal is transmitted to the semiconductor IC (integrated circuit) 249 according to conductive pattern from the external drive signal generating circuit 8 (see FIG. 12) and the head drive signal is supplied to each piezoelectric vibrator 239.
Thus, a plurality of pressure generating elements 17 (piezoelectric vibration units 238) and head drive circuits 18 (semiconductor ICs 249) are formed on the recording head 10 and mainly the transistors of the head drive circuits 18 (semiconductor ICs 249) generate heat and therefore hitherto, a heat radiation measure has been taken for the recording head 10.
That is, for the semiconductor IC (integrated circuit) 249 mounted on the flexible cable 242, the area exposed from the window 248 is fixed to the fix board 247 with an adhesive via a thermal-conductivity fluid layer (for example, silicon grease, etc.,) not shown or is fixed with an adhesive having high thermal conductivity to the fix board 247. The fix board 247 functions as a heat radiation member and is made of a material having high thermal conductivity such as metal or alumina. As shown in FIG. 13(A), the fix board 247 is placed close to the ink lead passage 245, whereby ink flowing through the ink lead passage 245 absorbs heat generated on the semiconductor IC 249 via the fix board 247.
At the printing time, upon reception of input of a print signal via the flexible cable 242 from the external drive signal generating circuit 8 (see FIG. 12), the semiconductor IC (integrated circuit) 249 generates a drive signal for driving each piezoelectric vibrator 239 and supplies the drive signal to each piezoelectric vibrator 239. Thus, mainly the transistors in the head drive circuit 18 generate heat and the heat has thermal conduction relationship with the semiconductor IC (integrated circuit) 249 forming the head drive circuit 18 and is absorbed by the heat sink action of the fix board 247 having a large heat capacity and is radiated through the fix board 247, so that the semiconductor IC (integrated circuit) 249 can be prevented from leading to thermal runaway or damage.
In the conventional art example described above, the recording head 10 is provided with the head drive circuit 18. However, if the drive signal COM is output from the apparatus main unit 2 to the recording head 10 with the long flexible wiring board 100, there is a problem of distorting the waveform of the drive signal COM because of parasitic inductance, etc., of the flexible wiring board 100. For the recording head 10, characteristics vary from one head to another, thus previous inspection is executed for ranking for matching with the drive signal COM, but the characteristics of the semiconductor IC 249 forming the drive signal generating circuit 8 also vary from one product to another, thus the drive signal COM output from the drive signal generating circuit 8 and the recording head 10 do not match in some cases.
In the conventional art example described above, as shown in FIGS. 13(A) and (B), the adjacent nozzle rows 232 and 232 each formed with a plurality of nozzle openings 231 are formed comparatively close to each other in the nozzle plate 233, thus it is feared that to jet an ink drop from a predetermined nozzle opening 231 in one nozzle row 232, vibration excited by the corresponding piezoelectric vibration unit 238 may affect the other nozzle row 232 (pressure generating chamber 234) and an ink drop whose amount is extremely small may be jetted from the nozzle opening 231 in the other nozzle row 232, causing erroneous print to occur.
Further, combined with high image quality of print precision, the number of nozzle openings 231 in one nozzle row 232 is increased, for example, from 32 to 64 and can become 128 or more, thus it is expected that the number of transistors integrated in the semiconductor IC (integrated circuit) 249 will also never grow, thus a further heat radiation measure in the recording head 10 is desired.
It is therefore a first object of the present invention to provide an ink jet recording apparatus having a configuration wherein distorting the waveform of a drive signal can be prevented and a recording head also containing a drive signal generating circuit can be tested.
It is a second object of the present invention to provide an ink jet recording apparatus having a configuration wherein vibration excited by a piezoelectric vibration unit 238 can be effectively prevented from affecting another nozzle row, causing erroneous print to occur.
Further, it is a third object of the present invention to provide an ink jet recording apparatus having a configuration wherein the heat radiation effect in a recording head 10 can be more enhanced and particularly the detrimental effect when the configuration to accomplish the first object is adopted can be avoided.
To achieve the first object, according to the present invention, there is provided an ink jet recording apparatus comprising a recording head comprising a plurality of pressure generating elements for pressurizing ink in pressure generating chambers, thereby jetting ink drops from nozzle openings and a head drive circuit for selecting which of the plurality of pressure generating elements a drive signal is to be applied to based on recording data and a drive signal generating circuit for outputting the drive signal, the drive signal generating circuit comprising at least a waveform generating circuit for generating the drive signal and a current amplification circuit for executing current amplification of the drive signal generated by the waveform generating circuit and outputting the result, characterized in that the current amplification circuit is formed on a side of the recording head.
In the present invention, the current amplification circuit corresponding to the last stage, of the drive signal generating circuit is formed in the recording head, so that the drive signal after undergoing current amplification is output to the head drive circuit in the recording head and is not output via the flexible wiring board connecting the apparatus main unit and the recording head. Therefore, a problem of distorting the waveform of the drive signal after undergoing current amplification because of parasitic inductance, etc., of the flexible wiring board can be solved. When the recording head is tested for characteristics, the recording head also containing the current amplification circuit of the drive signal generating circuit is tested for characteristics, so that the characteristics of the recording head also containing those of the drive signal generating circuit can be determined properly. Therefore, a proper drive signal can be applied to each pressure generating element in the recording head.
Here, if the current amplification circuit is formed in the recording head, heat generation of the recording head becomes large. In the present invention, however, the heat radiation member is placed in the recording head to achieve the third object, so that a temperature rise in the recording head can be prevented. Therefore, in the recording head, each circuit can be prevented from malfunctioning or being degraded because of heat, and the detrimental effect of hastening drying of ink in the presence of heat or the like can be avoided.
In the present invention, preferably the waveform generating circuit is also formed on the side of the recording head. In such a configuration, the drive signal before undergoing current amplification is also output to the head drive circuit in the recording head and is not output via the flexible wiring board connecting the apparatus main unit and the recording head. Therefore, a problem of distorting the waveforms of the drive signals before and after undergoing current amplification because of parasitic inductance, etc., of the flexible wiring board can be solved. When the recording head is tested for characteristics, the recording head also containing the waveform generating circuit and the current amplification circuit of the drive signal generating circuit is tested for characteristics, so that the characteristics of the recording head also containing those of the drive signal generating circuit can be determined properly. Therefore, a proper drive signal can be applied to each pressure generating element in the recording head.
To achieve the second object, in the present invention, preferably the nozzle openings are formed in a flow passage unit as a plurality of nozzle rows in parallel and the heat radiation member is in contact with at least the area corresponding to the area between the plurality of nozzle rows in the flow passage unit. In such a configuration, interference occurring between the nozzle rows can be suppressed by means of the heat radiation member.
To achieve the third object, in the present invention, the heat radiation member may comprise at least a horizontal plate section in face contact with a carriage on which the recording head is mounted and a vertical plate section extended so as to be in contact with the area corresponding to the area between the nozzle rows in the flow passage unit from the horizontal plate section, and an IC, in which at least the head drive circuit and the current amplification circuit are formed, may be mounted onto the vertical plate section. In such a configuration, the carriage and the heat radiation member can be brought into contact with each other for escaping heat from the heat radiation member to the carriage, so that a temperature rise in the recording head can be prevented. Therefore, in the recording head, each circuit can be prevented from malfunctioning or being degraded because of heat, and the detrimental effect of hastening drying of ink in the presence of heat or the like can be avoided.
In the present invention, preferably heat radiation fins are formed in the carriage. In such a configuration, a temperature rise in the recording head can be suppressed furthermore effectively.
In the present invention, preferably, using the fact that the current amplification circuit is formed in the recording head, output of the waveform generating circuit is input into the current amplification circuit via switching elements of the switch circuit of the head drive circuit. In such a configuration, a signal before undergoing current amplification is input into the switching elements of the head drive circuit, thus heat generation of the switching elements of the head drive circuit is small. Therefore, small-sized elements can be used as the switching elements of the head drive circuit.
To achieve the third object, according to another aspect of the present invention, there is provided an ink jet recording apparatus comprising a recording head comprising a plurality of pressure generating elements for pressurizing ink introduced into pressure generating chambers via an ink lead passage, thereby jetting ink drops from nozzle openings and a semiconductor device containing a head drive circuit for selecting which of the plurality of pressure generating elements a drive signal is to be applied to based on recording data and a drive signal generating circuit for outputting the drive signal, the drive signal generating circuit comprising at least a waveform generating circuit for generating the drive signal and a current amplification circuit for executing current amplification of the drive signal generated by the waveform generating circuit and outputting the result, characterized in that
the current amplification circuit and the waveform generating circuit are also formed so as to be contained in the semiconductor device of the recording head, and
the recording head has a heat radiation member for the semiconductor device.
In the present invention, preferably the heat radiation member comprises at least a horizontal plate section in face contact with a carriage on which the recording head is mounted and a vertical plate section extended from the horizontal plate section to the flow passage unit, and
the semiconductor device is mounted onto the vertical plate section.
Further, in the present invention, preferably a first heat insulation material is attached between the vertical plate section of the heat radiation member and the area corresponding to the area between the nozzle rows in the flow passage unit. The first heat insulation material thermally insulates the vertical plate section and the flow passage unit and the heat generated by the semiconductor device of the recording head is escaped upwardly through the vertical plate section of the heat radiation member and is effectively radiated through the horizontal plate section of the heat radiation member. Since the heat insulation material is provided, the heat generated by the semiconductor device can be efficiently prevented from being transmitted to the ink flow passage.
In the present invention, preferably the heat resistance ratio between the first heat insulation material and the heat radiation member is at least larger than 4:1, because if the heat generated by the IC reaches 150xc2x0 C., for example, the heat transmitted to the flow passage unit side can be suppressed to ⅕ or less.
In the present invention, preferably the ink lead passage is placed away from the semiconductor device. Further, in the present invention, the ink lead passage may be placed so as to be extended up and down between the semiconductor device and the pressure generating element. Since the ink lead passage is placed away from the semiconductor device (heat source), the heat generated by the semiconductor device (heat source) can be prevented from being transmitted to the ink flow passage. On the other hand, in the present invention, the surroundings of the semiconductor device may be covered with a second heat insulation material. Heat conduction to the ink lead passage is furthermore suppressed and it is also made possible to escape heat to the upper side more reliably.
In the present invention, first heat radiation fins may be formed in the carriage. Heat is radiated furthermore effectively through the first heat radiation fins of the carriage from the horizontal plate section of the heat radiation member.
In the present invention, second heat radiation fins may be formed on the upper surface side of the horizontal plate section of the heat radiation member. Thus, the heat radiation effect can be enhanced furthermore.
Preferably, in the present invention, the second heat radiation fins are formed in parallel in a move direction of the carriage, other fins are formed lower than the two fins at both ends so that only the two fins at both ends support an ink tank made of a resin for supplying ink to the ink lead passage of the recording head, and a space is provided between other fins and a bottom of the ink tank. While heat conduction to the ink tank is suppressed because the resin has a heat insulation effect, wind flows through the space between other fins and the bottom of the ink tank as the carriage is moved, so that the heat radiation effect is enhanced dramatically.